Method and apparatus for laying hot blacktop paving material

ABSTRACT

A method of laying hot blacktop paving material, the method comprising a spreading step during which the material is spread onto a surface for receiving it, and immediately prior to the spreading step, a step of adding water during which water plus wetting agent is mixed with the blacktop material.

[0001] The present invention relates to methods and apparatuses forlaying blacktop paving material while hot.

[0002] More particularly, the invention relates to a method of laying ablacktop material while hot (i.e. at a temperature above the ambienttemperatures commonly encountered in temperate countries), whichmaterial comprises bitumen-coated aggregate, the method including aspreading step during which said blacktop material is spread onto asurface that is to receive it, e.g. a road or the like.

BACKGROUND OF THE INVENTION

[0003] A blacktop material that is laid while hot always comprises a mixof a mineral aggregate skeleton coated in hot bitumen. Attempts are madeto keep its temperature high until it has finished being laid, whichgenerally occurs within the two hours following fabrication andtransport to the site where it is laid. This laying consists indistributing the mixture over the surface to be covered in a layer ofthickness that is defined, regular, and uniform, e.g. in order toconstitute a layer of a roadway (a top layer or a bed layer) or of asimilar work. The hot blacktop material is generally laid using a roadsurfacing machine which performs all of the mechanical functions thatare required, and that are accompanied in the final stage by passingcompactors over the freshly-spread layer, which compactors serve todensify the mixture.

[0004] During these various stages, it can happen that the temperatureof the mixture drops below the acceptable limit for satisfactory laying.In addition, it can be advantageous to fabricate paving material atrelatively low temperature, for example as described in the patentapplication filed on the same day as the present patent application bythe same Applicant.

OBJECTS AND SUMMARY OF THE INVENTION

[0005] A particular object of the invention is to improve the ease ofhandling of the blacktop paving material in order to make it easier tolay, in particular in the above-mentioned circumstances of laying at lowtemperature (but not exclusively in such circumstances).

[0006] To this end, according to the invention, a method of the kind inquestion further comprises, immediately before the spreading step, astep of adding water during which water plus wetting agent is mixed withthe blacktop material.

[0007] By means of these dispositions, it has been found that the easeof handling of the blacktop material is considerably improved bycreating an emulsion of water in bitumen, of the water-in-oil type, thusmaking spreading and distribution easier and compacting satisfactoryeven when the blacktop material is at relatively low temperature.

[0008] In preferred embodiments of the invention, recourse mayoptionally further be had to one or more of the following dispositions:

[0009] the water plus wetting agent presents a molar concentration ofwetting agent lying in the range 0.1% to 1.5%;

[0010] during the step of adding water, the water plus wetting agent isadded to the blacktop material at a weight concentration of 1% to 5%relative to the weight of the blacktop material;

[0011] the water plus wetting agent is mixed with the blacktop materialby kneading;

[0012] the bitumen of the blacktop material is in a non-foamy fluidstate during the steps of adding water and spreading;

[0013] the blacktop material is at a temperature lying in the range 60°C. to 100° C. during the steps of adding water and spreading; and

[0014] the blacktop material is at a temperature lying in the range 100°C. to 130° C., and preferably about 110° C. during the steps of addingwater and spreading.

[0015] Furthermore, the invention also provides apparatus forimplementing the method as defined above, the apparatus comprising mixermeans receiving the blacktop material and provided with at least onewater inlet fed with water plus wetting agent, and a spreader devicereceiving the material from the mixer means and adapted to spread theblacktop material. Advantageously, the apparatus includes metering meansfor metering out the water plus wetting agent.

BRIEF DESCRIPTION OF THE DRAWING

[0016] Other characteristics and advantages of the invention appear fromthe following description of an embodiment thereof given by way ofnon-limiting example and with reference to the accompanying drawing.

[0017] In the drawing, FIG. 1 is an outline diagram showing anembodiment of apparatus for implementing the method of the invention.

MORE DETAILED DESCRIPTION

[0018] The purpose of the method of the invention is to make it easy tolay blacktop paving material comprising bitumen-coated aggregate, and todo so in particular at relatively low temperature.

[0019] As shown in the drawing, the method of the invention can beimplemented, by way of example, using a road surfacing machine 1comprising:

[0020] a hopper 2 for receiving hot blacktop material, e.g. at atemperature lying in the range 60° C. to 140° C., for example in therange 600 to 100° C., or in the range 100° C. to 130° C., and preferablyabout 110° C., which material may be of the non-foamed type, forexample;

[0021] a conveyor 3 such as a conveyor belt which transfers the blacktoppaving material generally from the receiving hopper 2 in a rearwarddirection, i.e. in the direction opposite to the direction A in whichthe machine 1 advances;

[0022] a kneader 4 or other mixer device which receives the blacktopmaterial from the conveyor 3 and which is provided with a device 5 forfeeding water plus additives, the additives including at least onewetting agent, the kneader being adapted to mix the blacktop materialwith the water plus wetting agent plus any other additives;

[0023] an engine unit 7 for driving the moving parts of the machine 1;and

[0024] spreader means for spreading the material and comprising:

[0025] one or more distributor screws 8 for distributing the material 6transversely over the entire spreading width, the material 6 beingpoured onto a surface 10 for receiving it on leaving the kneader orother mixer device 4; and

[0026] a floating table constituted by a smoothing beam 9 fitted withvibrators and/or tampers, either a rigid beam or a beam provided with aplurality of extensible portions enabling the spreading width to bevaried while maintaining the surface state and the thickness of thelayer 11 that has been distributed.

[0027] The water feed device 5 may comprise, for example, a tank 5 a ofwater plus wetting agents, a water feeder 5 b such as a plurality ofsprinkler strips or the like, and a variable rate metering pump 5 cwhich enables the water feeder 5 b to receive water from the tank 5 a.

[0028] By way of non-limiting example, the wetting agent used may be thesubstance sold under the trademark “CECA L200”.

[0029] The wetting agent may be mixed with the water at a molarconcentration lying in the range 0.1% to 1.5%, for example about 0.3%.

[0030] The water plus wetting agent may itself be added to the blacktopmaterial at a weight ratio of water to material lying in the range 0.5%to 5%, this weight ratio being controlled by the metering pump 5 c whichcan be servo-controlled, e.g. to the speed of advance of the machine 1and/or to the quantity of material being laid.

[0031] Mixing in the kneader or other mixer device can take placerelatively quickly, for example over a period of 10 seconds to 2minutes. The kneading may optionally be performed by means of a conveyorwormscrew that acts simultaneously as a conveyor and as a kneader. Saidmixing may also be performed by means of a transverse distributor screwsimilar to the above-mentioned distributor screw 8. Mixing may also beperformed, not in the machine 1, but optionally in apparatus (not shown)used for feeding the machine 1 with blacktop material.

[0032] In all cases, kneading takes place immediately prior to thespreading operations, i.e. immediately prior to passing into thedistributor screw 8 and under the smoothing beam 9 (i.e. a few secondsto less than 10 minutes before these operations, for example), andadvantageously on the site where laying is taking place.

What is claimed is:
 1. A method of laying hot blacktop paving materialcomprising bitumen-coated aggregate, the method comprising a spreadingstep during which said material is spread on a surface for receiving it,the method further comprising, immediately before the spreading step, astep of adding water during which water plus wetting agent is mixed withthe blacktop material.
 2. A method according to claim 1, in which thewater plus wetting agent presents a molar concentration of wetting agentlying in the range 0.1% to 1.5%.
 3. A method according to claim 1, inwhich, during the step of adding water, the water plus wetting agent isadded to the blacktop material at a weight concentration of 1% to 5%relative to the weight of the blacktop material.
 4. A method accordingto claim 1, in which the water plus wetting agent is mixed with theblacktop material by kneading.
 5. A method according to claim 1, inwhich the bitumen of the blacktop material is in a non-foamy fluid stateduring the steps of adding water and spreading.
 6. A method according toclaim 1, in which the blacktop material is at a temperature lying in therange 60° C. to 100° C. during the steps of adding water and spreading.7. A method according to claim 1, in which the blacktop material is at atemperature lying in the range 100° C. to 130° C., and preferably about110° C. during the steps of adding water and spreading.
 8. Apparatus forimplementing a method according to claim 1, the apparatus comprisingmixer means receiving the blacktop material and provided with at leastone water inlet fed with water plus wetting agent, and a spreader devicereceiving the material from the mixer means and adapted to spread theblacktop material.
 9. Apparatus according to claim 8, including meteringmeans for metering out the water plus wetting agent.